In comparison to the conventional poppet valve engines wherein the high pressure in the cylinder just pushes the valves harder against their seats without having effect on the valve actuation mechanism, in the rotary valve engines the basic problem is that the high pressure in the cylinder loads strongly the valve system; the rotary valve is pushed heavily against the cylinder head degrading the sealing quality and causing excessive friction and seizure; the strong forces acting on the rotary valve while it is moving, make things even worse. The deformation of the combustion chamber due to both, the high pressure and the temperature differences, substantially affects the sealing quality provided by the state-of-the-art rotary valves.